Piston



.Hime 24 1924.

L. H. FOMEROY PISTON 111| l I 1 I I a Filed Sent. 4. 1919 Patented June2d, 1324i-,

narra saai-fas satana casina.

LAURENCE HENRY POMEROY, F CLEVELAND', Omo, ASSIG'NOR T0' THE ALUMINUMCOMPANY 0F AMERICA, 0F PITTSBURGH, PENNSYLVANIA, ACORPORATION OFPENNSYLVANIA.

PIs'roN.

Application led September 4, 1919. Serial No. 321,696.

To all 'whom t may concern.' vision of a piston that will wear evenlyfrom 55 Be it lmown that l, LAURENCE HENRY end to end. oMERoY, a subjectof the King of Great Another object of the invention is the at- Britainand Ireland, residing at Cleveland, tainment of the ends above mentionedin an 5 in the county of Cuyahoga and State of integrally cast piston.-

Ohio, have invented certain new and useful These and other more or lessincidental e0 Improvements in Pistons, of which .the folobjects, areattained in the manner set forth lowing is a specification, referencebeing had in the follo-Wing description of the preferred therein to theaccompanying drawings. form of construction. This invention relatesmore'particularly J Tn the drawings, v

to pistons adaptedj for use in internal com- Fig. 1 is a vlew partly inside elevation 65 bustion engines or under conditions in which andpartly in section of a piston embodying the piston is subjected toconsiderable heat. the invention.

As is well known, the clearance with which' Fig. 2 is a section on theline 2-2, Fig. 1.

the pistons of internal combustion engines -My improvements areapplicable to pisare fitted is determined in a large measure tons ofvarious forms of construction but 70 by the difference' in thermalexpansion of in the drawings, for purposes of explanation,

. the piston and the cylinder wall. This dif- I have shown the inventionapplied to the ference in thermal expansion is due to the slipper typeof piston shown in United fact that the working temperature of theStates Letters Patent No. 1,294,833, to H.

piston is somewhat higher than that of the R. Ricardo. 75 cylinder walland, in some cases, to the use Referring in detail to the constructionilof dierent piston and cylinder materials lustrated, the piston has ahead section 1 having diitl'erent cov-efficients of thermalconcomprising a crown 1a and a side wall 1b ductivity'and expansion.Thus in the case which is formed with grooves to receive suitof pistonsof aluminum or magnesium alloysable packing rings 2, 2. The guidesec-tion so working in iron cylinders the co-eflicient of of the pistoncomprises diametrically oppoeXpansion of the aluminum or the magnesitecylinder-engaging slippers 3 and 4:. a sium being higher than that o-firon, it is pair of wrist pin bosses 5, 5 arranged benecessary to givethe pistons a larger cleartween the slippers, and a pair of webs 6, 6

ance than is required for iron pistons workwhich join the slippers andbosses together 85 ing in iron cylinders. This larger clearand extendupward and mergel with the ance, with pistons as heretofore constructed,crown and side wall of the head section of results in piston slap orknock when the the piston, the entire piston being cast in engine isrunning cold at starting and, in one. Aside from the rings 2, 2, onlythe fact, whenever the thermal conditions of the slipper parts 3, 4.-are designed to contact 90 cylinder and piston are such that the large`with the cylinder wall, the piston differing clearance required toobviate seizure at high in this respect from the prior trunk orskirttemperatures exists between the piston and ed pistons which have aguide part in the cylinder wall. form of a continuous sleeve or skirtthat One object 0f the present invention is the contacts with thecylinder wall on all sides. 95 provision of a piston of aluminum alloyor Tn the construction shown the slippers 3 other light weight metal,that will operate' and 4 arelnade unequal in size, the larger withoutpiston slap. i slipper 3 being designed to take the angular Anotherobject of the invention. is the thrust or reaction of the connecting roddurprovision of a piston so constructed that it ing theexplosion strokeof an internal com- 10o can be given a small workin clearance in.--bustion engine, while the smaller slipper 4 dependent of diiferences oft ermaleXpanis designed to take the angular thrust dursion of the pistonand the cylinder wall. ing the compression stroke of the engine.

A further object ofthe-invention is the The abo-ve described features ofthe conprovision'of a piston capable of adjusting struction arecharacteristic of the Ricardo 105 itself to the cylinder as wear occursof the slipper piston.` i piston or cylinder or both. My improvementsconstituting the present Another object of the invention is theproinvention are effected by forming the piston so that some part of theguide structure is capable of resiliently yielding at points between thecylinder-engaging surfaces on opposite sides of the wrist pin tocompensate for differences in thermal expansion of the piston andcylinder and I prefer to make the guide structure so that it will yieldmore readily between the wrist pin bosses and the .-yiinder-engagingsurface which takes the thrustl during the compression stroke ot thepiston, than between said bosses and the cylinder-engaging surface whichtakes the thrust during the explosion stroke. The means, when applied tothe` slipper type of piston illustrated, that the major yield shalloccur between the pin bosses 5 and the cylinder-engaging surface of theslipper 4, and in the construction illustrated I have made provision fora resilient yielding in the webs 6, 6 which permits movement of theslipper 4 toward and from the slipper 3. To secure relative movement ofthe slipper 4 in parallelism, the web structure is formed to yield intwo separated sections, which are preferably adjacent the respectiveends of the slipper.

In the constructionillustrated this is accomplished by forming each ofthe webs G with two parallel slots 7 and the slot 7 being open at itsupper end and closed at its lower end, while the slot 8 is closed at itsupper end and open at its lowerend. The slots 7 and 8 terminate at theirclosed ends with enlarged cylindrical aperatures 7n and 8a,respectively. @Thus it will be seen that the slipper 4 is supported byelongated strips or sections 9 of the webs 6, and each of the sections 9has reduced and weakened cross sections at 9a and 9b, so that anyyielding of the web structure is localized at these points 9L and 9b. i

My improved form of construction can be app-lied to pistons cast of anysuitable metal but it. is especially useful in connection with pistonsof aluminum alloy or other light metals having high co-efticients ofthermal expansion in comparison with iron as it makes it possible to titsuch pistons with as small a clearance as is possible with iron pistonsof prior forms of construction. ron pistons of internal combustionengines iitted with a clearance of 0.00075 inch per inch of pistondiameter are found to operate with substantial freedom from piston slap,and pistons of aluminum alloy made in accordance with my invention canreadily be operated with similar clearances. Indeed a still smallerclearance is made possible by my invention.

In the operation of aluminum pistons of my improved form ofconstruction, asuming a cold \working clearance of 0.00075 inch per inchof piston diameter, or less, to insure freedom. from piston slap whenstarting, as the engine heats up the excess expansion of the piston ascompared with th'e surrounding cylinder wall of iron will reduce thisclearance; but as the clearance approaches zero the construction of thepiston webs permits them to yield so as to compensate for the excessexpansion of the guide section of the piston and all danger of theseizing of the piston is obviated. ll'hen the engine is stopped and theparts again cool down the resilience of the web structure causes it toreturn to normal form and a suitable small clearance between the pistonguide and the cylinder wall is maintained. It will. of course, beunderstood that the piston head proper is given a smaller diameter thanthe guide and does not function as a guide. -\s has been explained theyielding of the web structure occurs at the points 9 and 9h adjacent tothe upper and lower parts of the slipper 4 so that the slipper 4 ismaintained in parallelism with the axis of the cylinder. This insuresuniform contact and wear throughout the full length of the slippers. Asonly a relatively light thrust, incident to the compression of thecombustible charge in the engine cylinder, is applied to the smallerslipper 4, the resilient web structure is able to sustain the stressesto which it is suhjected, it being possible, of course, to make theguide structure between the wrist pin bosses and the cylinder-engagingsurface ot the slipper 3 adequately strong to sustain the heavy thrustdue to the explosion of the engine charge. This is an important featureof my invention since in most, if not all, cases it is found that aconstruction that is capable of. yielding sufficiently to adequatelycompensate for differences of expansion, will fail if subjected to theangular thrust of the connecting rod in the working or explosion strokeof the piston.

lt is to be understood that the dimensions of the yieldable websections, as at 9a and 9", will be determined by the diameter of thepiston and other factors such as the compression pressure and themaximum engine speed, the requirements being that the web sections 9aand 9b yield suiliciently to prevent seizing under theJ pressure set upbetween the cylinder wall and the piston due to thermal expansion, butdo not yield too much under the thrust due to compression and inertia,and that they yield, whether under said expansion pressure or under thethrust due to compression and inertia, in a manner to maintain theslipper 4 parallel to the piston axis.

It will be seen that the amount of yielding in the piston webs will bedetermined` for the most part, by the cold working clearance of thepiston. By making this clearance sufficiently small the clearance willbe rendered nil when the parts heat up in operation and a resilientpressure of the slippers against 4the cylinder wall will be secured.

Under these conditions the resiliency of the piston web structure willinsure the maintenance of close workin contacts between the slippers andthe cylinder wall as wear of these parts occurs and, as above noted, themovement of the slipper 4 parallel to the piston axis will insure auniform contact and wear of the parts throughout the full lengths of theslippers. In other words, my resiliently yieldable piston structure, bycompensating for excess expansion of the piston, secures an automaticadjustment of the piston to the cylinder as wear occurs.

My improvements, while applicable in their broader aspects to othertypes of pistons, are especially applicable to the slipper type ofpiston illustrated and it will be seen that this is due, in part atleast, to the fact that the yieldable web parts have no contact with thecylinderwall and thus are free, in so far as the cylinder is concerned,to accommodate themselves to the movement of those parts which do engagethe cylinder.

It is obvious that my invention can be embodied in various forms ofconstruction and it is to be understood that it is not limu ited to theparticular construction illustrated inthe drawing except as specified inthe following claims.

What I claim is:

1. An integrally cast piston comprising a head, diametrically oppositeguide slippers, a pair of wrist pinbosses between the slippers and apair of webs joining the head, slippers and bosses together, said websbeing formed at points between the bosses and one of the slippers so asto resiliently yield and'permit movement of said slipper toward and fromthe other slipper.

2. An integrally cast piston com rising a head, diametrically oppositegui e slippers, a rpair of wrist pin bosses between the slippers and apair of webs joining the head,

slippers and bosses together, said webs bein formed at points betweenthe bosses an one ofthe slippers so yas to resilientl yield and permitmovement of said slipper 1n paralle lism toward and from thekotherslipper. 3. An integrally cast piston comprising a a pair of wrist.pinvbosses between the slippers anda pair of webs joiningthe head,slippers and bosses together, said 'webs being formed between the bossesand one of the slippers each with a pair of parallel slots of which oneis open at its. end adjacent Athe of head, diametrically opposite guideslippers',

5. A piston having a head and a guide l structure connected thereto,said guide struc- ,ture comprising diametrically opposite parts havingcylinder-engaging surfaces, wrist pin bosses, between said oppositeparts, and means for joining said bosses and cylinderengaging parts,said joining means being arranged not to engage the cylinder and theguide structure being adapted to resiliently yield to a greater extentbetween the pin bosses and one of said cylinder-engaging surfaces thanbetween the said pin bosses and the other cylinder-engaging surface.

6. A piston having a head and a guide structure connected thereto, saidguide structure comprising diametrically opposite slippers havingcylinder-engaging surfaces, wrist pin bosses between the slippers andmeans joining said bosses and sllppers together, the guide structurebeing adapted to resiliently yleld to a greater extent at points betweenthe pin bosses and the cylinderengaging surfaces of one slipper thanbetween the said pin bosses and the cylinderengaging surfaces of theother slipper.

7. A piston having a head and a guide structure connected thereto whichcomprises diametrically opposite cylinder-engaging parts, wrist pinbosses between the cylinderengaging parts, and means joining said bossesand cylinder-engaging parts together,

the said joining means being resilientlyyieldable to a greater extent onone side of the wrist pin bosses than on the other side,

thereof.

8. A piston having a head and a guide structure connected thereto'whichcomprises v diametrically opposite slippers, wrist pin bosses betweenthe slippers and means joining said bosses and slippers together, thesaid joining means being resiliently yieldlable to a greater extent onone side of the wrist pin bosses thanon the other side therev`9. Apiston as claimed in claim 4 characterized by being integrally cast.

10. lA piston as claimed in claim 5 characterized by being integrallycast.

11. A piston as claimed in claim 6 characterized by being integrallycast.

j 12. A piston as claimed in claim 7 characterized by being integrallycast.

13. A piston as claimed in claim 8 characterized by bein integrallycast.

In testimony whereof, I hereunto ax my signature.

LAURENCE HENRY POMEROY.

